Cooling systems for internal combustion engines, including diesel engines, are well known in the art. Typically, such systems have employed a temperature sensitive valve (thermostat) to direct the flow of the coolant medium in the system through a heat exchanger (radiator) or through a bypass line around the heat exchanger. Such systems have successfully been employed in automobile engines and the like.
Advances over the years in engine technology, however, and particularly in diesel engine technology, have caused increasing demands to be placed on the cooling systems for internal combustion engines. For example, many diesel engines are now turbocharged. In compressing the air charged to the engine's cylinders, however, the turbocharger also causes the temperature of the air to increase. Accordingly, it is desirable to provide means for cooling the compressed air prior to its being charged to the cylinders, and thereby improve combustion efficiency, by means of a heat exchanger, commonly referred to as an aftercooler. The efficiency of the aftercooler depends in part on the difference in temperatures between the coolant and the compressed air; the greater the temperature potential, the greater will be the capability of the aftercooler in cooling the compressed air.
The cooling system should also be responsive to the engine's cooling demands under partial load conditions. Under partial load, the cooling requirement of the engine block and cylinder heads are less than the cooling requirements under full load; nevertheless, it may still be desirable to maintain maximum cooling efficiency of the aftercooler or other engine components. Accordingly, in order to maintain the engine at a relatively constant temperature, regardless of the load on the engine, and still satisfy the demands of the engine's other components, it is advantageous to provide the engine with a cooling system capable of regulating the amount of cooling to the engine by independently controlling the flow of coolant through the radiator and through the bypass line around the radiator.
Other important considerations in the design of an engine's cooling system relate to the design size of the engine's radiator. Typically, the radiator is made from expensive materials such as copper and aluminum. It is therefore highly desirable to minimize the size of the radiator, consistent with maintaining the ability of the radiator to handle the maximum design heat rejection load of the engine. As with an aftercooler, the efficiency of the radiator as a heat exchanger is dependent in part on the temperature difference or potential between the temperature of the coolant entering the radiator and the ambient air temperature. By maximizing this temperature potential, the engine designer can employ a smaller or more cost effective heat exchange unit.
The prior art has recognized some of the problems inherent in efficiently satisfying the various cooling demands of a diesel engine having an aftercooler. One attempt at solving these problems is described in U.S. Pat. No. 3,863,612 to Wiener. The Wiener patent ignores other features and elements of a diesel engine, however, which place additional demands upon and creates additional problems for the cooling system. For example, a modern diesel cooling system should be responsive to the demands of the engine's oil cooler, which is an important element for increasing the life and durability of the engine. The cooling system should also accommodate other elements, such as auxiliary heaters for the driver's cab and for the diesel fuel.
Moreover, to enhance the engine's efficiency when operating at cold ambient temperatures, and for smooth and efficient operation during start-up, the cooling system should also ideally be capable of not only cooling the engine, but of heating the engine's charge air as well. Also, because of changes in ambient temperature and the different demands on the cooling system during start-up, the cooling system should ideally have control logic which independently senses and anticipates the heating and the cooling demands of the engine.